Rapamycin inhibits F-actin reorganization and phosphorylation of focal adhesion proteins

New Wnt/β-catenin target genes promote experimental metastasis and migration of colorectal cancer cells through different signals

OBJECTIVES

We have previously identified a 115-gene signature that characterises the metastatic potential of human primary colon cancers. The signature included the canonical Wnt target gene BAMBI, which promoted experimental metastasis in mice. Here, we identified three new direct Wnt target genes from the signature, and studied their functions in epithelial-mesenchymal transition (EMT), cell migration and experimental metastasis.

DESIGN

We examined experimental liver metastases following injection of selected tumour cells into spleens of NOD/SCID mice. Molecular and cellular techniques were used to identify direct transcription target genes of Wnt/β-catenin signals. Microarray analyses and experiments that interfered with cell migration through inhibitors were performed to characterise downstream signalling systems.

RESULTS

Three new genes from the colorectal cancer (CRC) metastasis signature, BOP1, CKS2 and NFIL3, were identified as direct transcription targets of β-catenin/TCF4. Overexpression and knocking down of these genes in CRC cells promoted and inhibited, respectively, experimental metastasis in mice, EMT and cell motility in culture. Cell migration was repressed by interfering with distinct signalling systems through inhibitors of PI3K, JNK, p38 mitogen-activated protein kinase and/or mTOR. Gene expression profiling identified a series of migration-promoting genes, which were induced by BOP1, CKS2 and NFIL3, and could be repressed by inhibitors that are specific to these pathways.

CONCLUSIONS

We identified new direct Wnt/β-catenin target genes, BOP1, CKS2 and NFIL3, which induced EMT, cell migration and experimental metastasis of CRC cells. These genes crosstalk with different downstream signalling systems, and activate migration-promoting genes. These pathways and downstream genes may serve as therapeutic targets in the treatment of CRC metastasis.

Plasticity of tumor cell invasion: governance by growth factors and cytokines

Tumor cell migration, the basis for metastatic dissemination, is an adaptive process which depends upon coordinated cell interaction with the environment, influencing cell-matrix and cell-cell adhesion, cytoskeletal dynamics and extracellular matrix remodeling. Growth factors and cytokines, released within the reactive tumor microenvironment and their intracellular effector signals strongly impact mechanocoupling functions in tumor cells and thereby control the mode and extent of tumor invasion, including collective and single-cell migration and their interconversions. Besides their role in controlling tumor cell growth and survival, cytokines and growth factors thus provide complex orchestration of the metastatic cascade and tumor cell adaptation to environmental challenge. We here review the mechanisms by which growth factors and cytokines control the reciprocal interactions between tumor cells and their microenvironment, and the consequences for the efficacy and plasticity of invasion programs and metastasis.

Ciclopirox olamine inhibits mTORC1 signaling by activation of AMPK

Ciclopirox olamine (CPX), an off-patent antifungal agent, has recently been identified as a potential anticancer agent. The mammalian target of rapamycin (mTOR) is a central controller of cell growth, proliferation and survival. Little is known about whether and how CPX executes its anticancer action by inhibiting mTOR. Here we show that CPX inhibited the phosphorylation of p70 S6 kinase 1 (S6K1) and eukaryotic initiation factor 4E binding protein 1 (4E-BP1), two downstream effector molecules of mTOR complex 1 (mTORC1), in a spectrum of human tumor cells, indicating that CPX inhibits mTORC1 signaling. Using rhabdomyosarcoma cells as an experimental model, we found that expression of constitutively active mTOR (E2419K) conferred resistance to CPX inhibition of cell proliferation, suggesting that CPX inhibition of mTORC1 contributed to its anticancer effect. In line with this, treatment with CPX inhibited tumor growth and concurrently suppressed mTORC1 signaling in RD xenografts. Mechanistically, CPX inhibition of mTORC1 was neither via inhibition of IGF-I receptor or phosphoinositide 3-kinase (PI3K), nor by activation of phosphatase and tensin homolog (PTEN). Instead, CPX inhibition of mTORC1 was attributed to activation of AMP-activated protein kinase (AMPK)-tuberous sclerosis complexes (TSC)/raptor pathways. This is supported by the findings that CPX activated AMPK; inhibition of AMPK with Compound C or ectopic expression of dominant negative AMPKα partially prevented CPX from inhibiting mTORC1; silencing TSC2 attenuated CPX inhibition of mTORC1; and CPX also increased AMPK-mediated phosphorylation of raptor (S792). Therefore, the results indicate that CPX exerts the anticancer effect by activating AMPK, resulting in inhibition of mTORC1 signaling.

A novel derivative of betulinic acid, SYK023, suppresses lung cancer growth and malignancy

Herein, we evaluated the anti-cancer effect and molecular mechanisms of a novel betulinic acid (BA) derivative, SYK023, by using two mouse models of lung cancer driven by KrasG12D or EGFRL858R. We found that SYK023 inhibits lung tumor proliferation, without side effects in vivo or cytotoxicity in primary lung cells in vitro. SYK023 triggered endoplasmic reticulum (ER) stress. Blockage of ER stress in SYK023-treated cells inhibited SYK023-induced apoptosis. In addition, we found that the expression of cell cycle-related genes, including cyclin A2, B1, D3, CDC25a, and CDC25b decreased but, while those of p15INK4b, p16INK4a, and p21CIP1 increased following SYK023 treatment. Finally, low doses of SYK023 significantly decreased lung cancer metastasis in vitro and in vivo. Expression of several genes related to cell migration, including synaptopodin, were downregulated by SYK023, thereby impairing F-actin polymerization and metastasis. Therefore, SYK023 may be a potentially therapeutic treatment for metastatic lung cancer.

Suppression of the invasive potential of Glioblastoma cells by mTOR inhibitors involves modulation of NFκB and PKC-α signaling

Glioblastoma (GBM) is the most aggressive type of brain tumors in adults with survival period <1.5 years of patients. The role of mTOR pathway is documented in invasion and migration, the features associated with aggressive phenotype in human GBM. However, most of the preclinical and clinical studies with mTOR inhibitors are focused on antiproliferative and cytotoxic activity in GBM. In this study, we demonstrate that mTOR inhibitors-rapamycin (RAP), temisirolimus (TEM), torin-1 (TOR) and PP242 suppress invasion and migration induced by Tumor Necrosis Factor-α (TNFα) and tumor promoter, Phorbol 12-myristate 13-acetate (PMA) and also reduce the expression of the TNFα and IL1β suggesting their potential to regulate factors in microenvironment that support tumor progression. The mTOR inhibitors significantly decreased MMP-2 and MMP-9 mRNA, protein and activity that was enhanced by TNFα and PMA. The effect was mediated through reduction of Protein kinase C alpha (PKC-α) activity and downregulation of NFκB. TNFα- induced transcripts of NFκB targets -VEGF, pentraxin-3, cathepsin-B and paxillin, crucial in invasion were restored to basal level by these inhibitors. With limited therapeutic interventions currently available for GBM, our findings are significant and suggest that mTOR inhibitors may be explored as anti-invasive drugs for GBM treatment.

Both mTORC1 and mTORC2 are involved in the regulation of cell adhesion

mTOR is a central controller for cell growth/proliferation and survival. Recent studies have shown that mTOR also regulates cell adhesion, yet the underlying mechanism is not known. Here we found that inhibition of mTOR by rapamycin reduced the basal or type I insulin-like growth factor (IGF-1)-stimulated adhesion of cancer cells. Further research revealed that both mTORC1 and mTORC2 were involved in the regulation of cell adhesion, as silencing expression of raptor or rictor inhibited cell adhesion. Also, PP242, an mTORC1/2 kinase inhibitor, inhibited cell adhesion more potently than rapamycin (mTORC1 inhibitor). Of interest, ectopic expression of constitutively active and rapamycin-resistant mutant of p70 kinase 1 (S6K1) or downregulation of eukaryotic initiation factor 4E (eIF4E)-binding protein 1 (4E-BP1) conferred resistance to rapamycin inhibition of cell adhesion, whereas expression of constitutively hypophosphorylated 4E-BP1 (4EBP1-5A) or downregulation of S6K1 suppressed cell adhesion. In contrast, neither genetic manipulation of Akt activity nor pharmacological inhibition of Akt affected cell adhesion. The results suggest that both mTORC1 and mTORC2 are involved in the regulation of cell adhesion; and mTORC1 regulates cell adhesion through S6K1 and 4E-BP1 pathways, but mTORC2 regulates cell adhesion via Akt-independent mechanism.

Rapamycin inhibits mSin1 phosphorylation independently of mTORC1 and mTORC2

Current knowledge indicates that the mammalian target of rapamycin (mTOR) functions as two complexes, mTORC1 and mTORC2, regulating cell growth, proliferation, survival, differentiation, and motility. Recently mSin1 has been identified as a critical component of mTORC2, which is essential for phosphorylation of Akt and other signaling molecules. Studies have shown that rapamycin inhibits phosphorylation of mSin1. However, the underlying mechanism is unknown. Here we found that rapamycin inhibited phosphorylation of mSin1 potently and rapidly. Expression of rapamycin-resistant mutant of mTOR (mTOR-T), but not rapamycin-resistant and kinase dead mutant of mTOR (mTOR-TE), prevented rapamycin from inhibiting mSin1 phosphorylation, suggesting that rapamycin-induced dephosphorylation of mSin1 is mTOR-dependent. Surprisingly, ectopic expression of rapamycin-resistant and constitutively active p70 S6 kinase 1 (S6K1) did not confer resistance to rapamycin-induced dephosphorylation of mSin1. Furthermore, disruption of mTORC1 and mTORC2 by silencing raptor and rictor, respectively, or downregulation of S6K1 or Akt did not induce the dephosphorylation of mSin1 as rapamycin did. However, silencing mTOR or mLST8 mimicked the effect of rapamycin, inhibiting mSin1 phosphorylation. Our findings suggest that rapamycin inhibits mSin1 phosphorylation, which is independent of mTORC1 and mTORC2, but is possibly dependent on a new mTOR complex, which at least contains mTOR and mLST8.

Neuritic complexity of hippocampal neurons depends on WIP-mediated mTORC1 and Abl family kinases activities

INTRODUCTION

Neuronal morphogenesis is governed mainly by two interconnected processes, cytoskeletal reorganization, and signal transduction. The actin-binding molecule WIP (Wiskott-Aldrich syndrome protein [WASP]-interacting protein) was identified as a negative regulator of neuritogenesis. Although WIP controls activity of the actin-nucleation-promoting factor neural WASP (N-WASP) during neuritic differentiation, its implication in signal transduction remains unknown.

METHODS

Using primary neurons from WIP-deficient and wild-type mice we did an immunofluorescence, morphometric, and biochemical analysis of the signaling modified by WIP deficiency.

RESULTS

Here, we describe the WIP contribution to the regulation of neuritic elaboration and ramification through modification in phosphorylation levels of several kinases that participate in the mammalian target of rapamycin complex 1 (mTORC1)-p70S6K (phosphoprotein 70 ribosomal protein S6 kinase, S6K) intracellular signaling pathway. WIP deficiency induces an increase in the number of neuritic bifurcations and filopodial protrusions in primary embryonic neurons. This phenotype is not due to modifications in the activity of the phosphoinositide 3 kinase (PI3K)-Akt pathway, but to reduced phosphorylation of the S6K residues Ser(411) and Thr(389). The resulting decrease in kinase activity leads to reduced S6 phosphorylation in the absence of WIP. Incubation of control neurons with pharmacological inhibitors of mTORC1 or Abl, two S6K regulators, conferred a morphology resembling that of WIP-deficient neurons. Moreover, the preferential co-distribution of phospho-S6K with polymerized actin is altered in WIP-deficient neurons.

CONCLUSION

These experiments identify WIP as a member of a signaling cascade comprised of Abl family kinases, mTORC1 and S6K, which regulates neuron development and specifically, neuritic branching and complexity. Thus, we postulated a new role for WIP protein.

Infralimbic EphB2 Modulates Fear Extinction in Adolescent Rats

Adolescent rats are prone to impaired fear extinction, suggesting that mechanistic differences in extinction could exist in adolescent and adult rats. Since the infralimbic cortex (IL) is critical for fear extinction, we used PCR array technology to identify gene expression changes in IL induced by fear extinction in adolescent rats. Interestingly, the ephrin type B receptor 2 (EphB2), a tyrosine kinase receptor associated with synaptic development, was downregulated in IL after fear extinction. Consistent with the PCR array results, EphB2 levels of mRNA and protein were reduced in IL after fear extinction compared with fear conditioning, suggesting that EphB2 signaling in IL regulates fear extinction memory in adolescents. Finally, reducing EphB2 synthesis in IL with shRNA accelerated fear extinction learning in adolescent rats, but not in adult rats. These findings identify EphB2 in IL as a key regulator of fear extinction during adolescence, perhaps due to the increase in synaptic remodeling occurring during this developmental phase.

Select nutrients and their effects on conceptus development in mammals

The dialogue between the mammalian conceptus (embryo/fetus and associated membranes) involves signaling for pregnancy recognition and maintenance of pregnancy during the critical peri-implantation period of pregnancy when the stage is set for implantation and placentation that precedes fetal development. Uterine epithelial cells secrete and/or transport a wide range of molecules, including nutrients, collectively referred to as histotroph that are transported into the fetal-placental vascular system to support growth and development of the conceptus. The availability of uterine-derived histotroph has long-term consequences for the health and well-being of the fetus and the prevention of adult onset of metabolic diseases. Histotroph includes numerous amino acids, but arginine plays a particularly important role as a source of nitric oxide and polyamines required for fetal-placental development in rodents, swine and humans through mechanisms that remain to be fully elucidated. Mechanisms whereby arginine regulates expression of genes via the mechanistic target of rapamycin cell signaling pathways critical to conceptus development, implantation and placentation are discussed in detail in this review.

Annexin A1 Preferentially Predicts Poor Prognosis of Basal-Like Breast Cancer Patients by Activating mTOR-S6 Signaling

Introduction

Annexin A1 (ANXA1) is an anti-inflammatory protein reported to play a role in cell proliferation and apoptosis, and to be deregulated in breast cancer. The exact role of annexin A1 in the biology of breast cancer remains unclear. We hypothesized that the annexin A1 plays an oncogenic role in basal subtype of breast cancer by modulating key growth pathway(s).

Methods

By mining the Cancer Genome Atlas (TCGA)-Breast Cancer dataset and manipulating annexin A1 levels in breast cancer cell lines, we studied the role of annexin A1 in breast cancer and underlying signaling pathways.

Results

Our in-silico analysis of TCGA-breast cancer dataset demonstrated that annexin A1 mRNA expression is higher in basal subtype compared to luminal and HER2 subtypes. Within the basal subtype, patients show significantly poorer overall survival associated with higher expression of annexin A1. In both TCGA patient samples and cell lines, annexin A1 levels were significantly higher in basal-like breast cancer than luminal and Her2/neu-positive breast cancer. Stable annexin A1 knockdown in TNBC cell lines suppressed the mTOR-S6 pathway likely through activation of AMPK but had no impact on the MAPK, c-Met, and EGFR pathways. In a cell migration assay, annexin A1-depleted TNBC cells showed delayed migration as compared to wild-type cells, which could be responsible for poor patient prognosis in basal like breast cancers that are known to express higher annexin A1.

Conclusions

Our data suggest that annexin A1 is prognostic only in patients with basal like breast cancer. This appears to be in part due to the role of annexin A1 in activating mTOR-pS6 pathway.

Rapamycin prevents cadmium-induced neuronal cell death via targeting both mTORC1 and mTORC2 pathways

Cadmium (Cd), a toxic environmental contaminant, contributes to neurodegeneration. Rapamycin, a macrocyclic lactone, has shown preventive effect on Cd-induced neuronal cell death. However, the underlying mechanism is not fully understood. Here, we show that rapamycin prevented Cd-induced apoptotic cell death in neuronal cells. Coincidently, rapamycin markedly blocked Cd-induced phosphorylation of Akt, S6K1 and 4E-BP1 in the cells. Expression of a rapamycin-resistant and kinase-active mTOR (S2035T, mTOR-T), but not a rapamycin-resistant and kinase-dead mTOR (S2035T/D2357E, mTOR-TE), conferred resistance to rapamycin inhibition of Cd-induced cell death, implying that the preventive effect of rapamycin on Cd-induced neurotoxicity is mTOR kinase activity-dependent. It appeared that both mTORC1 and mTORC2 were involved in the inhibitory activity of rapamycin, as silencing raptor, rictor or raptor/rictor enhanced rapamycin's blockage of Cd-induced cell death. Furthermore, downregulation of S6K1, ectopic expression of constitutively hypophosphorylated 4E-BP1 or dominant negative Akt, or co-treatment with Akt inhibitor also potentiated the rapamycin's inhibitory effect. The findings indicate that rapamycin prevents Cd-induced neuronal cell death via suppressing both mTORC1 and mTORC2 pathways. Our results highlight that rapamycin may be exploited for the prevention of Cd-induced neurodegenerative disorders.

The interaction of protein-tyrosine phosphatase α (PTPα) and RACK1 protein enables insulin-like growth factor 1 (IGF-1)-stimulated Abl-dependent and -independent tyrosine phosphorylation of PTPα

Protein tyrosine phosphatase α (PTPα) promotes integrin-stimulated cell migration in part through the role of Src-phosphorylated PTPα-Tyr(P)-789 in recruiting and localizing p130Cas to focal adhesions. The growth factor IGF-1 also stimulates PTPα-Tyr-789 phosphorylation to positively regulate cell movement. This is in contrast to integrin-induced PTPα phosphorylation, that induced by IGF-1 can occur in cells lacking Src family kinases (SFKs), indicating that an unknown kinase distinct from SFKs can target PTPα. We show that this IGF-1-stimulated tyrosine kinase is Abl. We found that PTPα binds to the scaffold protein RACK1 and that RACK1 coordinates the IGF-1 receptor, PTPα, and Abl in a complex to enable IGF-1-stimulated and Abl-dependent PTPα-Tyr-789 phosphorylation. In cells expressing SFKs, IGF-1-stimulated phosphorylation of PTPα is mediated by RACK1 but is Abl-independent. Furthermore, expressing the SFKs Src and Fyn in SFK-deficient cells switches IGF-1-induced PTPα phosphorylation to occur in an Abl-independent manner, suggesting that SFK activity dominantly regulates IGF-1/IGF-1 receptor signaling to PTPα. RACK1 is a molecular scaffold that integrates growth factor and integrin signaling, and our identification of PTPα as a RACK1 binding protein suggests that RACK1 may coordinate PTPα-Tyr-789 phosphorylation in these signaling networks to promote cell migration.

An eIF4E-interacting peptide induces cell death in cancer cell lines

The eukaryotic initiation factor eIF4E is essential for cap-dependent initiation of translation in eukaryotes. Abnormal regulation of eIF4E has been implicated in oncogenic transformation. We developed an eIF4E-binding peptide derived from Angel1, a partner of eIF4E that we recently identified. We show here that this peptide fused to a penetratin motif causes drastic and rapid cell death in several epithelial cancer cell lines. This necrotic cell death was characterized by a drop in ATP levels with F-actin network injury being a key step in extensive plasma membrane blebbing and membrane permeabilization. This synthetic eIF4E-binding peptide provides a candidate pharmacophore for a promising new cancer therapy strategy.

Rotenone induction of hydrogen peroxide inhibits mTOR-mediated S6K1 and 4E-BP1/eIF4E pathways, leading to neuronal apoptosis

Rotenone, a common pesticide and inhibitor of mitochondrial complex I, induces loss of dopaminergic neurons and consequential aspects of Parkinson's disease (PD). However, the exact mechanism of rotenone neurotoxicity is not fully elucidated. Here, we show that rotenone induced reactive oxygen species (ROS), leading to apoptotic cell death in PC12 cells and primary neurons. Pretreatment with catalase (CAT), a hydrogen peroxide-scavenging enzyme, attenuated rotenone-induced ROS and neuronal apoptosis, implying hydrogen peroxide (H₂O₂) involved, which was further verified by imaging intracellular H₂O₂ using a peroxide-selective probe H2DCFDA. Using thenoyltrifluoroacetone (TTFA), antimycin A, or Mito-TEMPO, we further demonstrated rotenone-induced mitochondrial H₂O₂-dependent neuronal apoptosis. Rotenone dramatically inhibited mTOR-mediated phosphorylation of S6K1 and 4E-BP1, which was also attenuated by CAT in the neuronal cells. Of interest, ectopic expression of wild-type mTOR or constitutively active S6K1, or downregulation of 4E-BP1 partially prevented rotenone-induced H₂O₂ and cell apoptosis. Furthermore, we noticed that rotenone-induced H₂O₂ was linked to the activation of caspase-3 pathway. This was evidenced by the finding that pretreatment with CAT partially blocked rotenone-induced cleavages of caspase-3 and poly (ADP-ribose) polymerase. Of note, zVAD-fmk, a pan caspase inhibitor, only partially prevented rotenone-induced apoptosis in PC12 cells and primary neurons. Expression of mTOR-wt, S6K1-ca, or silencing 4E-BP1 potentiated zVAD-fmk protection against rotenone-induced apoptosis in the cells. The results indicate that rotenone induction of H₂O₂ inhibits mTOR-mediated S6K1 and 4E-BP1/eIF4E pathways, resulting in caspase-dependent and -independent apoptosis in neuronal cells. Our findings suggest that rotenone-induced neuronal loss in PD may be prevented by activating mTOR signaling and/or administering antioxidants.

Biological activities of fusarochromanone: a potent anti-cancer agent

Background

Fusarochromanone (FC101) is a small molecule fungal metabolite with a host of interesting biological functions, including very potent anti-angiogenic and direct anti-cancer activity.

Results

Herein, we report that FC101 exhibits very potent in-vitro growth inhibitory effects (IC₅₀ ranging from 10nM-2.5 μM) against HaCat (pre-malignant skin), P9-WT (malignant skin), MCF-7 (low malignant breast), MDA-231 (malignant breast), SV-HUC (premalignant bladder), UM-UC14 (malignant bladder), and PC3 (malignant prostate) in a time-course and dose-dependent manner, with the UM-UC14 cells being the most sensitive. FC101 induces apoptosis and an increase in proportion of cells in the sub-G1 phase in both HaCat and P9-WT cell lines as evidenced by cell cycle profile analysis. In a mouse xenograft SCC tumor model, FC101 was well tolerated, non-toxic, and achieved a 30% reduction in tumor size at a dose of 8 mg/kg/day. FC101 is also a potent anti-angiogenenic agent. At nanomolar doses, FC101 inhibits the vascular endothelial growth factor-A (VEGF-A)-mediated proliferation of endothelial cells.

Conclusions

Our data presented here indicates that FC101 is an excellent lead candidate for a small molecule anti-cancer agent that simultaneously affects angiogenesis signaling, cancer signal transduction, and apoptosis. Further understanding of the underlying FC101’s molecular mechanism may lead to the design of novel targeted and selective therapeutics, both of which are pursued targets in cancer drug discovery.

mTOR regulate EMT through RhoA and Rac1 pathway in prostate cancer

Recently, an increasing number of studies have suggested that mTOR plays a critical role in the regulation of tumor cell motility, invasion and cancer metastasis. However, little is known about the signaling mechanisms in regulating epithelial-mesenchymal transition (EMT) of prostate cancer. In this study, we found that the expression levels of Raptor and Rictor in prostate cancer tissues were elevated, which may suggest that Raptor and Rictor signaling pathways are associated with prostate cancer progression and metastasis. Inhibition of mTORC1 or mTORC2 by knock down of Raptor or Rictor, respectively, migration and invasion of prostate cancer were attenuated. Furthermore, EMT, a characterized by the changed expression levels of various markers like E-cadherin, β-catenin, N-cadherin, and vimentin emergend following inhibition of Raptor or Rictor. Finally, the small GTPases (RhoA and Rac1) which were crucial regulatory proteins in cell migration and invasion were inactivited after downregulating Raptor and Rictor. These results suggest that mTOR regulate EMT at least in part by down regulation of RhoA and Rac1 signaling pathways. Our findings provide novel very attractive target strategies that the inhibition of mTOR signaling pathways may retard prostate cancer migration and invasion at early stages.

Activation of Rheb, but not of mTORC1, impairs spine synapse morphogenesis in tuberous sclerosis complex

Mutations in the Tsc1 or Tsc2 genes cause tuberous sclerosis complex (TSC). Tsc1 and Tsc2 proteins form a complex that inhibits mammalian target of rapamycin complex 1 (mTORC1) signalling through Rheb-GTPase. We found that Tsc2^+/− neurons showed impaired spine synapse formation, which was resistant to an mTORC1 inhibitor. Knockdown of mTOR also failed to restore these abnormalities, suggesting mTORC may not participate in impaired spinogenesis in Tsc2^+/− neurons. To address whether Rheb activation impairs spine synapse formation, we expressed active and inactive forms of Rheb in WT and Tsc2^+/− neurons, respectively. Expression of active Rheb abolished dendritic spine formation in WT neurons, whereas inactive Rheb restored spine synapse formation in Tsc2^+/− neurons. Moreover, inactivation of Rheb with farnesyl transferase inhibitors recovered spine synapse morphogenesis in Tsc2^+/− neurons. In conclusion, dendritic spine abnormalities in TSC neurons may be caused through activation of Rheb, but not through of mTORC1.

Heat shock protein 90 promotes epithelial to mesenchymal transition, invasion, and migration in colorectal cancer

Epithelial to mesenchymal transition (EMT), invasion, and motility are essential steps in colorectal cancer (CRC) metastasis regulated by HIF-1α and NF-κB. Since HSP90 activates HIF-1α and NF-κB, we hypothesized that inhibition of HSP90 leads to inhibition of HIF-1α and NF-κB resulting in inhibition of EMT, invasion, and motility. Treatment of colorectal cancer cell lines HT-29 and HCT-116 with ganetespib at 50 nM for 24 h inhibited EMT (downregulated vimentin and upregulated E-cadherin), matrigel invasion, and spheroid migration. Ganetespib treatment or HSP90 knockdown downregulated molecular pathways associated with EMT, invasion, and motility. The overexpression of HIF-1α or NF-κB resulted in increased EMT, invasion, and motility in both cell lines and these effects were inhibited by ganetespib. Similar effects were observed in animal xenografts treated with ganetespib. Taken together, our data demonstrate for the first time that inhibition of HSP90 downregulates both HIF-1α and NF-κB leading to inhibition of EMT, motility, and invasiveness in colorectal cancer.

Activation of AMPK and inactivation of Akt result in suppression of mTOR-mediated S6K1 and 4E-BP1 pathways leading to neuronal cell death in in vitro models of Parkinson's disease

Parkinson's disease (PD) is a neurodegenerative disorder characterized by loss of dopaminergic neurons. Dysregulation of mammalian target of rapamycin (mTOR) has been implicated in the pathogenesis of PD. However, the underlying mechanism is incompletely elucidated. Here, we show that PD mimetics (6-hydroxydopamine, N-methyl-4-phenylpyridine or rotenone) suppressed phosphorylation of mTOR, S6K1 and 4E-BP1, reduced cell viability, and activated caspase-3 and PARP in PC12 cells and primary neurons. Overexpression of wild-type mTOR or constitutively active S6K1, or downregulation of 4E-BP1 in PC12 cells partially prevented cell death in response to the PD toxins, revealing that mTOR-mediated S6K1 and 4E-BP1 pathways due to the PD toxins were inhibited, leading to neuronal cell death. Furthermore, we found that the inhibition of mTOR signaling contributing to neuronal cell death was attributed to suppression of Akt and activation of AMPK. This is supported by the findings that ectopic expression of constitutively active Akt or dominant negative AMPKα, or inhibition of AMPKα with compound C partially attenuated inhibition of phosphorylation of mTOR, S6K1 and 4E-BP1, activation of caspase-3, and neuronal cell death triggered by the PD toxins. The results indicate that PD stresses activate AMPK and inactivate Akt, causing neuronal cell death via inhibiting mTOR-mediated S6K1 and 4E-BP1 pathways. Our findings suggest that proper co-manipulation of AMPK/Akt/mTOR signaling may be a potential strategy for prevention and treatment of PD.

Role of mTOR downstream effector signaling molecules in Francisella tularensis internalization by murine macrophages

Francisella tularensis is an infectious, gram-negative, intracellular microorganism, and the cause of tularemia. Invasion of host cells by intracellular pathogens like Francisella is initiated by their interaction with different host cell membrane receptors and the rapid phosphorylation of different downstream signaling molecules. PI3K and Syk have been shown to be involved in F. tularensis host cell entry, and both of these signaling molecules are associated with the master regulator serine/threonine kinase mTOR; yet the involvement of mTOR in F. tularensis invasion of host cells has not been assessed. Here, we report that infection of macrophages with F. tularensis triggers the phosphorylation of mTOR downstream effector molecules, and that signaling via TLR2 is necessary for these events. Inhibition of mTOR or of PI3K, ERK, or p38, but not Akt signaling, downregulates the levels of phosphorylation of mTOR downstream targets, and significantly reduces the number of F. tularensis cells invading macrophages. Moreover, while phosphorylation of mTOR downstream effectors occurs via the PI3K pathway, it also involves PLCγ1 and Ca(2+) signaling. Furthermore, abrogation of PLC or Ca(2+) signaling revealed their important role in the ability of F. tularensis to invade host cells. Together, these findings suggest that F. tularensis invasion of primary macrophages utilize a myriad of host signaling pathways to ensure effective cell entry.

Celastrol prevents cadmium-induced neuronal cell death via targeting JNK and PTEN-Akt/mTOR network

Cadmium (Cd), a toxic environmental contaminant, induces neurodegenerative diseases. Celastrol, a plant-derived triterpene, has shown neuroprotective effects in various disease models. However, little is known regarding the effect of celastrol on Cd-induced neurotoxicity. Here, we show that celastrol protected against Cd-induced apoptotic cell death in neuronal cells. This is supported by the findings that celastrol strikingly attenuated Cd-induced viability reduction, morphological change, nuclear fragmentation, and condensation, as well as activation of caspase-3 in neuronal cells. Concurrently, celastrol remarkably blocked Cd-induced phosphorylation of c-Jun N-terminal kinase (JNK), but not extracellular signal-regulated kinases 1/2 and p38, in neuronal cells. Inhibition of JNK by SP600125 or over-expression of dominant negative c-Jun potentiated celastrol protection against Cd-induced cell death. Furthermore, pre-treatment with celastrol prevented Cd down-regulation of phosphatase and tensin homolog deleted on chromosome 10 (PTEN) and activation of phosphoinositide 3'-kinase/protein kinase B (Akt)/mammalian target of rapamycin (mTOR) signaling in neuronal cells. Over-expression of wild-type PTEN enhanced celastrol inhibition of Cd-activated Akt/mTOR signaling and cell death in neuronal cells. The findings indicate that celastrol prevents Cd-induced neuronal cell death via targeting JNK and PTEN-Akt/mTOR network. Our results strongly suggest that celastrol may be exploited for the prevention of Cd-induced neurodegenerative disorders. Celastrol, a plant-derived triterpene, has shown neuroprotective effects. However, little is known regarding the effect of celastrol on cadmium (Cd) neurotoxicity. This study underscores that celastrol prevents Cd-induced neuronal apoptosis via inhibiting activation of JNK (c-Jun N-terminal kinase) and Akt/mTOR network. Celastrol suppresses Cd-activated Akt/mTOR pathway by elevating PTEN (phosphatase and tensin homolog). The findings suggest that celastrol may be exploited for the prevention of Cd-induced neurodegenerative disorders.

Regulation of blood-testis barrier (BTB) dynamics during spermatogenesis via the "Yin" and "Yang" effects of mammalian target of rapamycin complex 1 (mTORC1) and mTORC2

In mammalian testes, haploid spermatozoa are formed from diploid spermatogonia during spermatogenesis, which is a complicated cellular process. While these cellular events were reported in the 1960s and 1970s, the underlying molecular mechanism(s) that regulates these events remained unexplored until the past ∼10 years. For instance, adhesion proteins were shown to be integrated components at the Sertoli cell-cell interface and/or the Sertoli-spermatid interface in the late 1980s. But only until recently, studies have demonstrated that some of the adhesion proteins serve as the platform for signal transduction that regulates cell adhesion. In this chapter, a brief summary and critical discussion are provided on the latest findings regarding these cell-adhesion proteins in the testis and their relationship to spermatogenesis. Moreover, antagonistic effects of two mammalian target of rapamycin (mTOR) complexes, known as mTORC1 and mTORC2, on cell-adhesion function in the testis are discussed. Finally, a hypothetic model is presented to depict how these two mTOR-signaling complexes having the "yin" and "yang" antagonistic effects on the Sertoli cell tight junction (TJ)-permeability barrier can maintain the blood-testis barrier (BTB) integrity during the epithelial cycle while preleptotene spermatocytes are crossing the BTB.

Dihydroartemisinin inhibits the mammalian target of rapamycin-mediated signaling pathways in tumor cells

Dihydroartemisinin (DHA), an antimalarial drug, has previously unrecognized anticancer activity, and is in clinical trials as a new anticancer agent for skin, lung, colon and breast cancer treatment. However, the anticancer mechanism is not well understood. Here, we show that DHA inhibited proliferation and induced apoptosis in rhabdomyosarcoma (Rh30 and RD) cells, and concurrently inhibited the signaling pathways mediated by the mammalian target of rapamycin (mTOR), a central controller for cell proliferation and survival, at concentrations (<3 μM) that are pharmacologically achievable. Of interest, in contrast to the effects of conventional mTOR inhibitors (rapalogs), DHA potently inhibited mTORC1-mediated phosphorylation of p70 S6 kinase 1 and eukaryotic initiation factor 4E binding protein 1 but did not obviously affect mTORC2-mediated phosphorylation of Akt. The results suggest that DHA may represent a novel class of mTORC1 inhibitor and may execute its anticancer activity primarily by blocking mTORC1-mediated signaling pathways in the tumor cells.

Neural nitric oxide synthase participates in pemphigus vulgaris acantholysis through upregulation of Rous sarcoma, mammalian target of rapamycin and focal adhesion kinase

Pemphigus vulgaris (PV) is an autoimmune blistering skin disease characterized by suprabasal acantholysis produced as a consequence of desmoglein (Dsg) and non-Dsg autoantibodies binding to several targeting molecules localized on the membrane of keratinocytes. Nitric oxide (NO) may exert a pathogenic function in several immunological processes. We have previously demonstrated that neural nitric oxide synthase (nNOS) plays part in PV acantholysis. Also, our group has described a relevant role for HER [human epidermal growth factor receptor (EGFR) related] isoforms and several kinases such as Src (Rous sarcoma), mammalian target of rapamycin (mTOR) and focal adhesion kinase (FAK), as well as caspases in PV development. Using a passive transfer mouse model of PV, we aimed to investigate the relationship between the increase in nNOS and EGFR, Src, mTOR and FAK kinase upregulation observed in PV lesions. Our results revealed a new function for nNOS, which contributes to EGFR-mediated PV acantholysis through the upregulation of Src, mTOR and FAK. In addition, we found that nNOS participates actively in PV at least in part by increasing caspase-9 and caspase-3 activities. These findings underline the important issue that in PV acantholysis, caspase activation is a nNOS-linked process downstream of Src, mTOR and FAK kinase upregulation.

Molecular mechanisms of asymmetric division in oocytes

In contrast to symmetric division in mitosis, mammalian oocyte maturation is characterized by asymmetric cell division that produces a large egg and a small polar body. The asymmetry results from oocyte polarization, which includes spindle positioning, migration, and cortical reorganization, and this process is critical for fertilization and the retention of maternal components for early embryo development. Although actin dynamics are involved in this process, the molecular mechanism underlying this remained unclear until the use of confocal microscopy and live cell imaging became widespread in recent years. Information obtained through a PubMed database search of all articles published in English between 2000 and 2012 that included the phrases "oocyte, actin, spindle migration," "oocyte, actin, polar body," or "oocyte, actin, asymmetric division" was reviewed. The actin nucleation factor actin-related protein 2/3 complex and its nucleation-promoting factors, formins and Spire, and regulators such as small GTPases, partitioning-defective/protein kinase C, Fyn, microRNAs, cis-Golgi apparatus components, myosin/myosin light-chain kinase, spindle stability regulators, and spindle assembly checkpoint regulators, play critical roles in asymmetric cell division in oocytes. This review summarizes recent findings on these actin-related regulators in mammalian oocyte asymmetric division and outlines a complete signaling pathway.

Prevention of F-actin assembly switches the response to SCF from chemotaxis to degranulation in human mast cells

Following antigen/IgE-mediated aggregation of high affinity IgE-receptors (FcεRI), mast cells (MCs) degranulate and release inflammatory mediators leading to the induction of allergic reactions including anaphylaxis. Migration of MCs to resident tissues and sites of inflammation is regulated by tissue chemotactic factors such as stem cell factor (SCF (KIT ligand)). Despite inducing similar early signaling events to antigen, chemotactic factors, including SCF, produce minimal degranulation in the absence of other stimuli. We therefore investigated whether processes regulating MC chemotaxis are rate limiting for MC mediator release. To investigate this issue, we disrupted actin polymerization, a requirement for MC chemotaxis, with latrunculin B and cytochalasin B, then examined chemotaxis and mediator release in human (hu)MCs induced by antigen or SCF. As expected, such disruption minimally affected early signaling pathways, but attenuated SCF-induced human mast cell chemotaxis. In contrast, SCF, in the absence of other stimuli, induced substantial degranulation in a concentration-dependent manner following actin disassembly. It also moderately enhanced antigen-mediated human mast cell degranulation which was further enhanced in the presence of SCF. These observations suggest that processes regulating cell migration limit MC degranulation as a consequence of cytoskeletal reorganization.

Proof-of-concept rare cancers in drug development: the case for rhabdomyosarcoma

Rare diseases typically affect fewer than 200,000 patients annually, yet because thousands of rare diseases exist, the cumulative impact is millions of patients worldwide. Every form of childhood cancer qualifies as a rare disease-including the childhood muscle cancer, rhabdomyosarcoma (RMS). The next few years promise to be an exceptionally good era of opportunity for public-private collaboration for rare and childhood cancers. Not only do certain governmental regulation advantages exist, but these advantages are being made permanent with special incentives for pediatric orphan drug-product development. Coupled with a growing understanding of sarcoma tumor biology, synergy with pharmaceutical muscle disease drug-development programs, and emerging publically available preclinical and clinical tools, the outlook for academic-community-industry partnerships in RMS drug development looks promising.

Dissecting the PI3K Signaling Axis in Pediatric Solid Tumors: Novel Targets for Clinical Integration

Children with solid tumors represent a unique population. Recent improvements in pediatric solid tumor survival rates have been confined to low- and moderate-risk cancers, whereas minimal to no notable improvement in survival have been observed in high-risk and advanced-stage childhood tumors. Treatments for patients with advanced disease are rarely curative, and responses to therapy are often followed by relapse, which highlights the large unmet need for novel therapies. Recent advances in cancer treatment have focused on personalized therapy, whereby patients are treated with agents that best target the molecular drivers of their disease. Thus, a better understanding of the pathways that drive cancer or drug resistance is of critical importance. One such example is the phosphatidylinositol 3-kinase (PI3K)/Akt/mammalian target of rapamycin (mTOR) pathway, which is activated in many solid cancer patients and represents a target for therapy. PI3K/Akt/mTOR pathway activation has also been observed in tumors resistant to agents targeting upstream receptor tyrosine kinases (RTKs). Agents that target this pathway have the potential to shut down survival pathways, and are being explored both in the setting of pathway-activating mutations and for their ability to restore sensitivity to upstream signaling targeted agents. Here, we examine the role of the PI3K/Akt/mTOR pathway in pediatric solid tumors, review the novel agents being explored to target this pathway, and explore the potential role of the inhibition of this pathway in the clinical development of these agents in children.

mTOR: a link from the extracellular milieu to transcriptional regulation of oligodendrocyte development

Oligodendrocyte development is controlled by numerous extracellular signals that regulate a series of transcription factors that promote the differentiation of oligodendrocyte progenitor cells to myelinating cells in the central nervous system. A major element of this regulatory system that has only recently been studied is the intracellular signalling from surface receptors to transcription factors to down-regulate inhibitors and up-regulate inducers of oligodendrocyte differentiation and myelination. The current review focuses on one such pathway: the mTOR (mammalian target of rapamycin) pathway, which integrates signals in many cell systems and induces cell responses including cell proliferation and cell differentiation. This review describes the known functions of mTOR as they relate to oligodendrocyte development, and its recently discovered impact on oligodendrocyte differentiation and myelination. A potential model for its role in oligodendrocyte development is proposed.

Prognostic significance and function of phosphorylated ribosomal protein S6 in esophageal squamous cell carcinoma

Ribosomal protein S6 is a key regulator of 40S ribosome biogenesis, and its phosphorylation is closely related to cell growth capacity. However, as a downstream target of S6 kinases, the clinical significance and the roles of S6 and S6 phosphorylation in cell viability and motility of esophageal squamous cell carcinoma remain unclear. Here, we show that high level of phosphorylated-ribosomal protein S6 (p-S6) (immunohistochemistry score ≥5) and an increased ratio of p-S6/S6 (immunohistochemistry score ≥0.75) were significantly associated with shortened disease-free survival in patients with esophageal squamous cell carcinoma in univariate analysis (P=0.049 and P<0.001, respectively). After adjusting for age, tumor-nodes-metastasis stage, chemotherapy, and radiation therapy in multivariate analysis, both p-S6 (hazard ratio 2.21, P=0.005) and p-S6/S6 (hazard ratio 2.40, P<0.001) remained independent adverse prognostic factors. In addition, S6 and S6 kinase 1 knockdown resulted in attenuation of viability by suppressing cyclin D1 expression in esophageal cancer cells. Furthermore, depletion of S6 and S6 kinase 1 resulted in a reduction in esophageal cancer cell migration and invasion. This was paralleled by a reduction in focal adhesion and by suppression of extracellular signal-regulated kinase and c-jun N-terminal kinase phosphorylation, which control cell motility. Collectively, these findings suggest that p-S6 and the ratio of p-S6/S6 are closely relevant to tumor progression and have prognostic significance in esophageal squamous cell carcinoma.

The microtubule binding drug EM011 inhibits the growth of paediatric low grade gliomas

Low grade gliomas are a heterogeneous group of tumours representing the most common form of neoplasms in the central nervous system among children. Although gross total resection remains the principal treatment, it is often impractical especially for the resection of tumours within eloquent regions of the brain. Instead Radiotherapy is utilised in such cases, but because of its associated toxicities, it is refrained from use among younger children. These limitations coupled with hypersensitivity and toxicities associated with some commonly used chemotherapeutic agents, have ignited the need to search for safer and more effective treatments for paediatric low grade gliomas. In this study, we investigated the EM011 drug on the growth of two pilocytic and one diffuse paediatric astrocytoma cell lines, using an assortment of cancer assays. We discovered that treatments of low grade gliomas with EM011 abrogated cell viability by inducing a decrease in cell proliferation and an arrest in the S and G2M cell cycle phases, followed by a converse increase in apoptosis in a dose and time dependent manner. The cell migratory and invasion indices, as well as anchorage independent growth in soft agarose, were significantly attenuated. These findings were mechanistically associated with a transient release of AIF, a disruption of microtubule architecture, and a decline in the expression of key genes which drive cancer progression including EGFR, mTORC1, JUN and multiple MMPs. In fact, the activity of MMP2 was also perturbed by EM011. These findings, in conjunction with the insignificant adverse side effects established from other studies, make EM011 an appealing chemotherapeutic agent for the treatment of paediatric low grade gliomas.

Regulation of actin dynamics and protein trafficking during spermatogenesis--insights into a complex process

In the mammalian testis, extensive restructuring takes place across the seminiferous epithelium at the Sertoli-Sertoli and Sertoli-germ cell interface during the epithelial cycle of spermatogenesis, which is important to facilitate changes in the cell shape and morphology of developing germ cells. However, precise communications also take place at the cell junctions to coordinate the discrete events pertinent to spermatogenesis, namely spermatogonial renewal via mitosis, cell cycle progression and meiosis, spermiogenesis and spermiation. It is obvious that these cellular events are intimately related to the underlying actin-based cytoskeleton which is being used by different cell junctions for their attachment. However, little is known on the biology and regulation of this cytoskeleton, in particular its possible involvement in endocytic vesicle-mediated trafficking during spermatogenesis, which in turn affects cell adhesive function and communication at the cell-cell interface. Studies in other epithelia in recent years have shed insightful information on the intimate involvement of actin dynamics and protein trafficking in regulating cell adhesion and communications. The goal of this critical review is to provide an updated assessment of the latest findings in the field on how these complex processes are being regulated during spermatogenesis. We also provide a working model based on the latest findings in the field including our laboratory to provide our thoughts on an apparent complicated subject, which also serves as the framework for investigators in the field. It is obvious that this model will be rapidly updated when more data are available in future years.

Beyond control of protein translation: what we have learned about the non-canonical regulation and function of mammalian target of rapamycin (mTOR)

Mammalian target of rapamycin (mTOR) is a serine-threonine kinase involved in almost every aspect of mammalian cell function. This kinase was initially believed to control protein translation in response to amino acids and trophic factors, and this function has become a canonical role for mTOR. However, mTOR can form two separate protein complexes (mTORCs). Recent advances clearly demonstrate that both mTORCs can respond to various stimuli and change myriad cellular processes. Therefore, our current view of the cellular roles of TORCs has rapidly expanded and cannot be fully explained without appreciating recent findings about the new modes of mTOR regulation and identification of non-canonical effectors of mTOR that contribute to transcription, cytoskeleton dynamics, and membrane trafficking. This review discusses the molecular details of these newly discovered non-canonical functions that allow mTORCs to control the cellular environment at multiple levels. This article is part of a Special Issue entitled: Inhibitors of Protein Kinases (2012).

miRNA-100 inhibits human bladder urothelial carcinogenesis by directly targeting mTOR

miRNAs are involved in cancer development and progression, acting as tumor suppressors or oncogenes. In this study, miRNA profiling was conducted on 10 paired bladder cancer tissues using 20 GeneChip miRNA Array, and 10 differentially expressed miRNAs were identified in bladder cancer and adjacent noncancerous tissues of any disease stage/grade. After being validated on expanded cohort of 67 paired bladder cancer tissues and 10 human bladder cancer cell lines by quantitative real-time PCR (qRT-PCR), it was found that miR-100 was downregulated most significantly in cancer tissues. Ectopic restoration of miR-100 expression in bladder cancer cells suppressed cell proliferation and motility, induced cell-cycle arrest in vitro, and inhibited tumorigenesis in vivo both in subcutaneous and in intravesical passage. Bioinformatic analysis showed that the mTOR gene was a direct target of miR-100. siRNA-mediated mTOR knockdown phenocopied the effect of miR-100 in bladder cancer cell lines. In addition, the cancerous metastatic nude mouse model established on the basis of primary bladder cancer cell lines suggested that miR-100/mTOR regulated cell motility and was associated with tumor metastasis. Both mTOR and p70S6K (downstream messenger) presented higher expression levels in distant metastatic foci such as in liver and kidney metastases than in primary tumor. Taken together, miR-100 may act as a tumor suppressor in bladder cancer, and reintroduction of this mature miRNA into tumor tissue may prove to be a therapeutic strategy by reducing the expression of target genes.

Select nutrients in the uterine lumen of sheep and pigs affect conceptus development

Interferon tau (IFNT) is the pregnancy recognition signal from ruminant conceptuses. IFNT also acts with P4 to induce expression of genes for transport of nutrients, such as glucose (Gluc) and arginine (Arg) into the uterine lumen to activate mechanistic mammalian target of rapamycin (MTOR) cell signaling that stimulates proliferation, migration, gene transcription and mRNA translation by conceptus trophectoderm (Tr). In ewes, Arg and Gluc increase significantly in the uterine lumen between Days 10 and 15 of pregnancy due to increased expression of transporters for Gluc (SLC2A1 and SLC5A1) and Arg (SLC7A2B) by uterine epithelia. Arg and Gluc stimulate proliferation, migration and mRNA translation by Tr. Arg increases expression of GTP cyclohydrolase 1 (GCH1) and IFNT mRNAs while Arg and Gluc increase ornithine decarboxylase, nitric oxide synthase 2, and GCH1 mRNAs and proteins by Tr cells. GCH1 is required for synthesis of tetrahydrobiopterin, an essential cofactor for all NOS isoforms. Arg is metabolized to nitric oxide and polyamines that increase proliferation and migration of Tr cells. In pigs, Gluc, Arg, leucine (Leu) and glutamine (Gln) increase in the uterine lumen between Days 12 and 15 of pregnancy due to enhanced expression of transporters for Gluc and amino acids. Transporters for Gluc in porcine uterine LE (SLC2A1) and conceptus trophectoderm (SLC2A2) are abundant. Transporters for glutamate and neutral (SLC1A1, SLC1A4) and cationic (SLC7A1, SLC7A2, SLC7A7, SLC7A9) amino acids are expressed in uterine LE and SLC7A3 mRNA is expressed in conceptus Tr. Arg and Leu increase MTOR cell signaling and proliferation of pig Tr, as do Gluc and fructose. Azaserine, an inhibitor of hexosamine biosynthesis, inhibits effects of Gluc and fructose. Thus, select nutrients in the uterine lumen affect gene transcription and mRNA translation to affect conceptus development.

Select nutrients, progesterone, and interferon tau affect conceptus metabolism and development

Interferon tau (IFNT), a novel multifunctional type I interferon secreted by trophectoderm, is the pregnancy recognition signal in ruminants that also has antiviral, antiproliferative, and immunomodulatory bioactivities. IFNT, with progesterone, affects availability of the metabolic substrate in the uterine lumen by inducing expression of genes for transport of select nutrients into the uterine lumen that activate mammalian target of rapamycin (mTOR) cell signaling responsible for proliferation, migration, and protein synthesis by conceptus trophectoderm. As an immunomodulatory protein, IFNT induces an anti-inflammatory state affecting metabolic events that decrease adiposity and glutamine:fructose-6-phosphate amidotransferase 1 activity, while increasing insulin sensitivity, nitric oxide production by endothelial cells, and brown adipose tissue in rats. This short review focuses on effects of IFNT and progesterone affecting transport of select nutrients into the uterine lumen to stimulate mTOR cell signaling required for conceptus development, as well as effects of IFNT on the immune system and adiposity in rats with respect to its potential therapeutic value in reducing obesity.

rpS6 Regulates blood-testis barrier dynamics by affecting F-actin organization and protein recruitment

During spermatogenesis, preleptotene spermatocytes residing near the basement membrane of the seminiferous tubule must traverse the blood-testis barrier (BTB) at stage VIII-IX of the epithelial cycle to continue their development in the adluminal compartment. Unlike other blood-tissue barriers (e.g. the blood-brain barrier) that are created by the endothelial tight junction (TJ) barrier of capillaries, the BTB is created by specialized junctions between Sertoli cells in which TJ coexists with basal ectoplasmic specialization (basal ES, a testis-specific adherens junction). The basal ES is typified by the presence of tightly packed actin filament bundles sandwiched between cisternae of endoplasmic reticulum and the apposing plasma membranes of Sertoli cells. These actin filament bundles also confer unusual adhesive strength to the BTB. Yet the mechanisms by which these filamentous actin (F-actin) networks are regulated from the bundled to the debundled state to facilitate the transit of spermatocytes remain elusive. Herein, we provide evidence that ribosomal protein S6 (rpS6), the downstream signaling molecule of the mammalian target of rapamycin complex 1 (mTORC1) pathway, is a major regulator of F-actin organization and adhesion protein recruitment at the BTB. rpS6 is restrictively and spatiotemporally activated at the BTB during the epithelial cycle. An activation of rpS6 led to a disruption of the Sertoli cell TJ barrier and BTB integrity. Its silencing in vitro or in vivo by using small interfering RNA duplexes or short hairpin RNA was found to promote the Sertoli cell TJ permeability barrier by the recruitment of adhesion proteins (e.g. claudin-11 and occludin) to the BTB. Thus, rpS6 in the mTORC1 pathway regulates BTB restructuring via its effects on the F-actin organization and protein recruitment at the BTB.

Keloid disease can be inhibited by antagonizing excessive mTOR signaling with a novel dual TORC1/2 inhibitor

Keloid disease (KD) is a fibroproliferative lesion of unknown etiopathogenesis that possibly targets the PI3K/Akt/mTOR pathway. We investigated whether PI3K/Akt/mTOR inhibitor, Palomid 529 (P529), which targets both mammalian target of rapamycin complex 1 (mTORC-1) and mTORC-2 signaling, could exert anti-KD effects in a novel KD organ culture assay and in keloid fibroblasts (KF). Treatment of KF with P529 significantly (P < 0.05) inhibited cell spreading, attachment, proliferation, migration, and invasive properties at a low concentration (5 ng/mL) and induced substantial KF apoptosis when compared with normal dermal fibroblasts. P529 also inhibited hypoxia-inducible factor-1α expression and completely suppressed Akt, GSK3β, mTOR, eukaryotic initiation factor 4E-binding protein 1, and S6 phosphorylation. P529 significantly (P < 0.05) inhibited proliferating cell nuclear antigen and cyclin D and caused considerable apoptosis. Compared with rapamycin and wortmannin, P529 also significantly (P < 0.05) reduced keloid-associated phenotypic markers in KF. P529 caused tissue shrinkage, growth arrest, and apoptosis in keloid organ cultures and substantially inhibited angiogenesis. pS6, pAkt-Ser473, and mTOR phosphorylation were also suppressed in situ. P529 reduced cellularity and expression of collagen, fibronectin, and α-smooth muscle actin (substantially more than rapamycin). These pre-clinical in vitro and ex vivo observations are evidence that the mTOR pathway is a promising target for future KD therapy and that the dual PI3K/Akt/mTOR inhibitor P529 deserves systematic exploration as a candidate agent for the future treatment of KD.

Clinicopathologic significance and function of mammalian target of rapamycin activation in esophageal squamous cell carcinoma

Mammalian target of rapamycin (mTOR) has emerged as a key regulator of cell metabolism, growth, and proliferation. Despite the increasing significance of mTOR signaling in cancer cell cycle and proliferation, the clinical significance of activated mTOR in esophageal squamous cell carcinoma and its role in esophageal cancer cell proliferation and invasion remain unclear. Here, we show that both high levels of phosphorylated-mTOR and an increased ratio of phosphorylated-mTOR/mTOR (ratio ≥0.2) were significantly associated with shortened disease-specific survival in 165 patients with esophageal squamous cell carcinoma in univariate analysis (P = .047 for phosphorylated-mTOR, P = .021 for phosphorylated-mTOR/mTOR); phosphorylated-mTOR and phosphorylated-mTOR/mTOR remained independent prognostic factors after adjusting for age, TNM stage, chemotherapy, and radiation therapy in multivariate analysis (hazard ratio, 1.67, P = .025 for phosphorylated-mTOR; hazard ratio, 1.95, P = .006 for phosphorylated-mTOR/mTOR). Moreover, down-regulation of mTOR or mTOR complex components led to attenuation of proliferation, migration, and invasion of esophageal squamous cell carcinoma cell lines through suppression of cyclin D1 expression. Collectively, our findings suggest that phosphorylated-mTOR and the ratio of phosphorylated-mTOR/mTOR are closely linked to tumor progression and represent independent prognostic factors in esophageal squamous cell carcinoma, thereby providing a potential therapeutic target for this malignancy.

microRNA-21 governs TORC1 activation in renal cancer cell proliferation and invasion

Metastatic renal cancer manifests multiple signatures of gene expression. Deviation in expression of mature miRNAs has been linked to human cancers. Importance of miR-21 in renal cell carcinomas is proposed from profiling studies using tumor tissue samples. However, the role of miR-21 function in causing renal cancer cell proliferation and invasion has not yet been shown. Using cultured renal carcinoma cells, we demonstrate enhanced expression of mature miR-21 along with pre-and pri-miR-21 by increased transcription compared to normal proximal tubular epithelial cells. Overexpression of miR-21 Sponge to quench endogenous miR-21 levels inhibited proliferation, migration and invasion of renal cancer cells. In the absence of mutation in the PTEN tumor suppressor gene, PTEN protein levels are frequently downregulated in renal cancer. We show that miR-21 targets PTEN mRNA 3'untranslated region to decrease PTEN protein expression and augments Akt phosphorylation in renal cancer cells. Downregulation of PTEN as well as overexpression of constitutively active Akt kinase prevented miR-21 Sponge-induced inhibition of renal cancer cell proliferation and migration. Moreover, we show that miR-21 Sponge inhibited the inactivating phosphorylation of the tumor suppressor protein tuberin and attenuated TORC1 activation. Finally, we demonstrate that expression of constitutively active TORC1 attenuated miR-21 Sponge-mediated suppression of proliferation and migration of renal cancer cells. Our results uncover a layer of post-transcriptional regulation of PTEN by transcriptional activation of miR-21 to force the canonical oncogenic Akt/TORC1 signaling conduit to drive renal cancer cell proliferation and invasion.

Mechanistic mammalian target of rapamycin (MTOR) cell signaling: effects of select nutrients and secreted phosphoprotein 1 on development of mammalian conceptuses

Morphological differentiation of uterine glands in mammals is a postnatal event vulnerable to adverse effects of endocrine disruptors. Exposure of ewe lambs to a progestin from birth to postnatal day 56 prevents development of uterine glands and, as adults, the ewes are unable to exhibit estrous cycles or maintain pregnancy. Uterine epithelia secrete proteins and transport nutrients into the uterine lumen necessary for conceptus development, pregnancy recognition signaling and implantation, including arginine and secreted phosphoprotein 1 (SPP1). Arginine can be metabolized to nitric oxide and to polyamines or act directly to activate MTOR cell signaling to stimulate proliferation, migration, and mRNA translation in trophectoderm cells. SPP1 binds αvβ3 and α5β1 integrins and induces focal adhesion assembly, adhesion and migration of conceptus trophectoderm cells during implantation. Thus, arginine and SPP1 mediate growth, migration, cytoskeletal remodeling and adhesion of trophectoderm essential for pregnancy recognition signaling and implantation.

Cryptotanshinone activates p38/JNK and inhibits Erk1/2 leading to caspase-independent cell death in tumor cells

Cryptotanshinone (CPT), a natural compound isolated from the plant Salvia miltiorrhiza Bunge, is a potential anticancer agent. However, the underlying mechanism is not well understood. Here, we show that CPT induced caspase-independent cell death in human tumor cells (Rh30, DU145, and MCF-7). Besides downregulating antiapoptotic protein expression of survivin and Mcl-1, CPT increased phosphorylation of p38 mitogen-activated protein kinase (MAPK) and c-jun N-terminal kinase (JNK), and inhibited phosphorylation of extracellular signal-regulated kinases 1/2 (Erk1/2). Inhibition of p38 with SB202190 or JNK with SP600125 attenuated CPT-induced cell death. Similarly, silencing p38 or c-Jun also in part prevented CPT-induced cell death. In contrast, expression of constitutively active mitogen-activated protein kinase kinase 1 (MKK1) conferred resistance to CPT inhibition of Erk1/2 phosphorylation and induction of cell death. Furthermore, we found that all of these were attributed to CPT induction of reactive oxygen species (ROS). This is evidenced by the findings that CPT induced ROS in a concentration- and time-dependent manner; CPT induction of ROS was inhibited by N-acetyl-L-cysteine (NAC), a ROS scavenger; and NAC attenuated CPT activation of p38/JNK, inhibition of Erk1/2, and induction of cell death. The results suggested that CPT induction of ROS activates p38/JNK and inhibits Erk1/2, leading to caspase-independent cell death in tumor cells.

Small-molecule screen identifies modulators of EWS/FLI1 target gene expression and cell survival in Ewing's sarcoma

Ewing's sarcoma family of tumors (EFT) is characterized by the presence of chromosomal translocations leading to the expression of oncogenic transcription factors such as, in the majority of cases, EWS/FLI1. Because of its key role in Ewing's sarcoma development and maintenance, EWS/FLI1 represents an attractive therapeutic target. Here, we characterize PHLDA1 as a novel direct target gene whose expression is repressed by EWS/FLI1. Using this gene and additional specific well-characterized target genes such as NROB1, NKX2.2 and CAV1, all activated by EWS/FLI1, as a read-out system, we screened a small-molecule compound library enriched for FDA-approved drugs that modulated the expression of EWS/FLI1 target genes. Among a hit-list of nine well-known drugs such as camptothecin, fenretinide, etoposide and doxorubicin, we also identified the kinase inhibitor midostaurin (PKC412). Subsequent experiments demonstrated that midostaurin is able to induce apoptosis in a panel of six Ewing's sarcoma cell lines in vitro and can significantly suppress xenograft tumor growth in vivo. These results suggest that midostaurin might be a novel drug that is active against Ewing's cells, which might act by modulating the expression of EWS/FLI1 target genes.

Paxillin phosphorylation and complexing with Erk and FAK are regulated by PLD activity in MDA-MB-231 cells

MDA-MB-231 cells are highly aggressive human breast adenocarcinoma cells that depend on PLD activity for survival. In response to the stress of serum withdrawal, there is increased motility and invasiveness of these cells that is associated with a rapid increase in PLD activity. In addition, PLD activity is elevated in response to most mitogenic signals. Similar to PLD, paxillin, a focal adhesion adaptor protein, and Erk, mitogen-activated protein kinase, play vital roles in cell motility through regulation of focal adhesion dynamics. Here, we addressed whether there is a functional correlation between paxillin and PLD that may influence cancer cell motility. We investigated the role of PLD activity on paxillin regulation, Erk activation and formation of a paxillin-Erk and paxillin-FAK association. Inhibition of PLD activity led to an increase in paxillin tyrosine phosphorylation, a decrease in Erk activation, as measured by phosphorylation, and enhanced association of paxillin with Erk. In addition, we found that paxillin tyrosine phosphorylation depends upon Erk activity and may be a consequence of an increased association with FAK. Taken together, these results suggest that Erk activity is governed by PLD activity and regulates the tyrosine phosphorylation of paxillin, potentially explaining its role in cell motility. This study indicated that PLD, Erk, paxillin and FAK participate in the same signaling pathway in this breast cancer cell line.

Inhibition of chemokine (CXC motif) ligand 12/chemokine (CXC motif) receptor 4 axis (CXCL12/CXCR4)-mediated cell migration by targeting mammalian target of rapamycin (mTOR) pathway in human gastric carcinoma cells

CXCL12/CXCR4 plays an important role in metastasis of gastric carcinoma. Rapamycin has been reported to inhibit migration of gastric cancer cells. However, the role of mTOR pathway in CXCL12/CXCR4-mediated cell migration and the potential of drugs targeting PI3K/mTOR pathway remains unelucidated. We found that CXCL12 activated PI3K/Akt/mTOR pathway in MKN-45 cells. Stimulating CHO-K1 cells expressing pEGFP-C1-Grp1-PH fusion protein with CXCL12 resulted in generation of phosphatidylinositol (3,4,5)-triphosphate, which provided direct evidence of activating PI3K by CXCL12. Down-regulation of p110β by siRNA but not p110α blocked phosphorylation of Akt and S6K1 induced by CXCL12. Consistently, p110β-specific inhibitor blocked the CXCL12-activated PI3K/Akt/mTOR pathway. Moreover, CXCR4 immunoprecipitated by anti-p110β antibody increased after CXCL12 stimulation and G(i) protein inhibitor pertussis toxin abrogated CXCL12-induced activation of PI3K. Further studies demonstrated that inhibitors targeting the PI3K/mTOR pathway significantly blocked the chemotactic responses of MKN-45 cells triggered by CXCL12, which might be attributed primarily to inhibition of mTORC1 and related to prevention of F-actin reorganization as well as down-regulation of active RhoA, Rac1, and Cdc42. Furthermore, rapamycin inhibited the secretion of CXCL12 and the expression of CXCR4, which might form a positive feedback loop to further abolish upstream signaling leading to cell migration. Finally, we found cells expressing high levels of cxcl12 were sensitive to rapamycin in its activity inhibiting migration as well as proliferation. In summary, we found that the mTOR pathway played an important role in CXCL12/CXCR4-mediated cell migration and proposed that drugs targeting the mTOR pathway may be used for the therapy of metastatic gastric cancer expressing high levels of cxcl12.

Rapamycin prevents endothelial cell migration by inhibiting the endothelial-to-mesenchymal transition and matrix metalloproteinase-2 and -9: an in vitro study

PURPOSE

To evaluate the influence of rapamycin on endothelial-mesenchymal transition and matrix metalloproteinase (MMP) secretion by human umbilical vein endothelial cell line EA.hy926 and explore rapamycin's angiogenesis inhibition mechanism.

METHODS

EA.hy926 cells were cultivated in vitro. After the cells attained complete confluency, an artificial scratch was made through the monolayer with a sterile plastic 100 μl micropipette tip. Cell morphology changes were observed. The expression of vascular endothelial (VE)-cadherin, vimentin, and Twist protein were examined by immunofluorescence. After scratching, the cells were treated with 10, 100, and 1,000 ng/ml rapamycin for durations of 24, 48, and 72 h. Cell proliferation was then assessed using methyl thiazolyl tetrazolium assay. Cell migration ability was examined, and the expression of VE-cadherin, vimentin, and the Twist transcription factor in mRNA levels was evaluated with reverse transcriptase PCR. The expression of gelatinases (MMP-2 and MMP-9) was examined using gelatin zymography.

RESULTS

After scratching, the endothelial cells were able to migrate via an endothelial-to-mesenchymal transition, which was related to Twist expression. Finally, mesenchymal cells transitioned into endothelial cells and reached cell confluency again. The growth of EA.hy926 cells was not affected by rapamycin concentrations of 10 ng/ml or 100 ng/ml during treatment periods of 1, 2, and 3 days; however, cell growth was inhibited by 1,000 ng/ml rapamycin with a three-day treatment period. Rapamycin successfully inhibited cell migration at concentrations of 10 ng/ml, 100 ng/ml, and 1,000 ng/ml for a treatment period of up to 8 h. Different concentrations of rapamycin induced the expression of VE-cadherin, inhibited vimentin and Twist expression in the endothelial cells, and inhibited endothelial cell secretion of MMP-2 and MMP-9.

CONCLUSIONS

Rapamycin inhibited cell migration and extracellular matrix degradation by inhibiting endothelial-to-mesenchymal transition and the endothelial cell secretion of MMP-2 and MMP-9; these may be possible mechanisms for the inhibition of angiogenesis by rapamycin.